Transformation of a Pd6 trifacial barrel to a Pd8 tetrafacial barrel by C70 as guest and oxidative photolysis of alkenes using the C70 encapsulated barrel under red light

Abstract

Fabricating discrete molecular cages as fullerene receptors has been a compelling task. The main objective of confining fullerene molecules is to utilize their physicochemical properties in commonly used media in which they are insoluble. Herein, a fluorenone-based large trigonal Pd6 molecular barrel (M1) was synthesized by coordination self-assembly to act as a potential fullerene trap. M1 in the presence of fullerene C70, converted to a larger Pd8 tetrafacial barrel (M2) forming stable host-guest adduct, (C70)3@M2. The PF6ˉ analogues of both M1 and (C70)3@M2 were acetonitrile soluble, generated reactive oxygen species due to the presence of photosensitizing fluorenone backbone and catalyzed the oxidative transformation of alkenes to carbonyl compounds under 390 nm irradiation. The presence of encapsulated C70 molecules in (C70)3@M2 enabled its photosensitizing wavelength to be tuned to 650 nm (red light). Subsequently, (C70)3@M2 at low catalyst loading and red light irradiation, catalyzed olefin oxidations in acetonitrile wherein free C70 was completely inefficient due to insolubility. In summary, (C70)3@M2 was employed as a photocatalyst to mimic the ozonolysis of olefins without the use of ozone or other metal-oxide oxidants that produces over-oxidized products and generates toxic wastes, under innocuous red light irradiation and in environment-friendly reaction conditions.